Capability Analysis (Poisson) - Tests
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Stat > Quality Control > Capability Analysis > Poisson > Tests

With Capability Analysis (Poisson), you can perform the four tests for special causes. Each test, as shown in the table below, detects a specific pattern in the plotted data. The occurrence of a pattern suggests a special cause for the variation that should be further investigated.

You can set preferences for the tests to perform and for the sensitivity of these tests using Tools > Options > Control Charts and Quality Tools > Tests.

When a point fails a test, it is marked with the test number on the plot. If a point fails more than one test, the number of the first test you request is the number printed on the plot. Minitab prints a summary table in the Session window with the complete information.

Test 1    One point more than 3 sigmas from center line

Test 2    Nine points in a row on same side of center line

image\QCTEST1.gif

image\QCTEST2.gif

Test 3    Six points in a row, all increasing or decreasing

Test 4    Fourteen points in a row, alternating up and down

image\QCTEST3.gif

image\QCTEST4.gif

Dialog box items

Tests For Special Causes: Enter the number of tests you want performed in the P chart portion of the report.

Perform all four tests: Choose to perform all four tests shown below.

Choose specific tests to perform: Choose to specify a subset of the four tests, then check any combination of the tests listed below.

One point more than 3 sigmas from center line

Nine points in a row on same side of center line

Six points in a row, all increasing or all decreasing

Fourteen points in a row, alternating up and down